Micro Coaxial Cable factory

Demystifying Micro Coaxial Cable Color Coding Standards

Micro coaxial cables, essential for transmitting high-frequency signals in tightly packed modern electronics, often rely on color coding for quick identification of connector shells (often ground) and center conductors during installation and repair. Unlike larger coaxial standards (like RG-6 for cable TV), micro coaxial color coding isn’t universally mandated by a single global body. However, distinct conventions and de facto standards have emerged, making understanding them crucial for engineers, technicians, and procurement specialists.

Common Standardized Color Schemes

1. ​50 Ohm Characteristic Impedance (Common Electronics & RF):
   • ​RG174 / M17/74-RG174 / UG-936: This extremely common micro coax frequently uses ​white for the outer jacket. The inner insulator surrounding the center conductor is often ​clear or translucent, and the center conductor itself is typically ​silver-plated copper (visible through the insulation). The connector shells are almost universally ​gold (or nickel) plated brass. Specific pin colors within the connector often follow signal assignment, not strictly coax identification.
   • ​RG178 / M17/78-RG178: This thinner alternative often features a ​silver-coated copper braid visible under a ​clear or blue outer jacket. The center conductor is commonly ​silver-plated copper clad steel (SPCCS) with a clear inner insulator. Connector shells remain gold/nickel plated.
   • ​RG316 / M17/116-RG316: This slightly thicker option may use ​white, blue, or black for the outer jacket. The center conductor is usually ​silver-plated copper, and the inner insulator is commonly ​semi-rigid PTFE (Teflon), often white. Connector shells are gold/nickel plated.
   ​Key Takeaway: For these standard military-spec (MIL) derived types (RG174/178/316), the outer jacket color (white being predominant for RG174, blue common for RG178/316) and the clear inner insulation revealing the center conductor are the most consistent visual identifiers. Connector shells are distinct but not color-coded per coax type.
2. ​75 Ohm Characteristic Impedance (Video Applications – e.g., Miniature Camera Links):
   • ​RG179: Used where impedance matching is critical for video signals, RG179 often employs a ​black outer jacket. The center conductor is frequently ​copper, and the inner insulator may be ​foamed or solid polyethylene, potentially ​colored white or black. Connector shells remain gold/nickel plated.
   • ​Non-Standard Color Use: Some manufacturers may produce RG174 in black specifically for 75-ohm video applications, distinguishing it from their standard 50-ohm white version. Always check specifications! Some vendors offer ​RG179 with a distinct blue jacket as well.
   ​Key Takeaway: Black jackets are very common for 75-ohm micro coax like RG179 used in video. However, overlap exists (e.g., RG174 can be 50Ω or 75Ω; RG316 often blue for 50Ω), making jacket color ​a guide, not a guarantee. Measurement or specification checking is vital.

The Prevalence of Non-Standard & Manufacturer-Specific Color Codes

Due to the lack of an overriding standard for micro coax colors themselves (beyond common MIL types) and the custom needs of complex assemblies, non-standard or bespoke color schemes are widespread:

1. ​Internal Wiring Harnesses: Manufacturers designing multi-cable harnesses (e.g., for laptops, medical sensors, drone cameras) often assign arbitrary but consistent colors to individual micro coax assemblies purely for internal traceability. A blue micro coax might carry one specific signal, yellow another, regardless of the underlying coax type (which might all be RG174). Documenting this within the harness drawing is paramount.
2. ​Connector Pin Insulation: The color of the plastic insulator around the crimp pin inside the connector (e.g., MMCX, MCX, SMPM) is almost always chosen to signify ​signal function or polarity within the specific device (e.g., red for +V, black for GND, green for data), rather than identifying the coax cable type itself. The coaxial cable attaches to this pin.
3. ​Manufacturer Branding/Identification: Some cable manufacturers use unique outer jacket colors (e.g., specific shades of blue, purple, red) as a brand identifier or to denote a proprietary cable construction, even if the electrical specs match a standard like RG316.
4. ​Strain Relief Boots: Colored flexible plastic strain relief boots covering the back of the connector are extremely common and useful for strain relief and identification. These are ​NOT a standard for the coax cable itself but are assigned by the harness designer or manufacturer. A red boot doesn’t mean “RG179”, it likely means “Signal Path A” or “Antenna 1” in that specific application.

Practical Implications and How to Handle Ambiguity

1. ​Never Assume by Color Alone: As shown, jacket color (e.g., white, black, blue) can be used across different cable types (50Ω vs 75Ω) and different manufacturers. Center conductor insulation colors vary significantly.
2. ​Prioritize Specifications and Markings:
   • ​Cable Markings: Look for text printed directly on the outer jacket (e.g., “RG174/U”, “RG316”, “50 OHM”, “75 OHM”, “M17/78-RG178”).
   • ​Manufacturer Datasheets: Always refer to the datasheet provided with the cable assembly or the raw cable for definitive identification, including impedance, attenuation, conductor material, and exact dimensions.
   • ​Harness Documentation: If part of a larger assembly, the wiring diagram or harness assembly drawing is the ​only definitive source for what each colored cable or colored strain relief boot signifies in that specific product.
   • ​Physical Measurement: If documentation is missing, carefully measuring the outer diameter (OD) can help distinguish (e.g., RG178 ~1.8mm vs RG174 ~2.6mm vs RG316 ~2.7mm), though color will not.
   • ​Electrical Testing: Using a Time-Domain Reflectometer (TDR) or network analyzer is the most accurate way to measure characteristic impedance if unknown.
3. ​Function Over Color: Focus on identifying the cable’s ​function within its application (e.g., “this is the main antenna feedline”, “this is the high-speed camera data link”). Its electrical specs (impedance, attenuation) are far more critical than its color.

Conclusion: Color is a Tool, Not a Rule

While recognizable patterns exist (e.g., common white RG174), color coding in micro coaxial cables serves primarily as an assembly aid and visual differentiation tool within harnesses or specific manufacturer lines, not as a universally reliable, stand-alone identifier of the cable’s intrinsic electrical specifications (like impedance). The jacket color and center conductor visibility (clear insulation) provide clues, especially for common MIL-derived 50Ω cables. However, ambiguity is high, especially distinguishing 50Ω vs 75Ω or identifying custom variants. Success hinges on combining visual observation with rigorous reference to cable markings, manufacturer specifications, assembly documentation, and appropriate testing. When in doubt, always ​consult the documentation or perform electrical measurements.